It is known to create a liquid/gas mixture by delivering a generally cohesive sheet of liquid into a stream of gas flowing through a passage, with the gas acting to shear liquid droplets away from the sheet of liquid. Such a liquid/gas mixture has been found to have a significantly smaller average liquid droplet size than that produced by delivering liquid under pressure through a restricted nozzle to form a spray as many commonly available motor vehicle injectors operate. A liquid/gas mixing apparatus which operates by shearing liquid droplets away from a sheet of liquid is disclosed in U.S. Pat. No. 5,735,468 and which is incorporated herein by reference.
Due to the very small size of the liquid droplets, the liquid/gas mixture produced by shearing liquid droplets from a sheet of liquid using a stream of gas can be delivered along a passage beyond the point at which the liquid is sheared from the sheet, and out through a nozzle.
If a nozzle has a simple continuous expansion zone leading to its outlet, it has been found that such a nozzle delivering liquid/gas mixtures tends to adhere liquid to and build up liquid on the inside surface of the expansion zone, and which liquid is pushed along the passage and out from the outlet as relatively large droplets as compared with the fine mist entrained in the stream of gas flowing into the nozzle.
It would be desirable to eliminate or at least minimize such adherence, build up and delivery of liquid droplets from the nozzle outlet.
The above and other objects and advantages of the present invention are achieved by the provision of a nozzle arrangement for delivering a liquid/gas mixture which comprises a plurality of nozzle assemblies. Each nozzle assembly has a body which includes a flow-through passage leading to an outlet, an expansion zone proximate the outlet, and at least one discontinuity in the expansion zone formed as a radially extending step-wise enlargement followed by a parallel-sided cylindrical portion extending toward the outlet. The discontinuity is adapted to reduce liquid film adherence at the outlet, and the nozzle assemblies are axially aligned and spaced apart by respective gas and/or liquid inspiration zones.
Preferably each discontinuity is substantially of circumferential extent.
The expansion zone preferably has a plurality of discontinuities.
Preferably, the flow passage also has a restriction or compression zone spaced upstream from the expansion zone. The restriction or compression zone is preferably a smoothly converging portion of the flow passage, and which leads to a throat portion which is intermediate the restriction zone and the expansion zone.
The flow passage is preferably generally circular in cross-section as is each expansion zone.
The or each step-wise enlargement in the expansion zone is/are preferably in the form of a circumferential edge having a first diameter, a radially outwardly extending surface which is generally normal to the central axis of the flow passage, and an axially extending cylindrical surface having a second diameter which is a predetermined amount larger than the first diameter, and which leads to the next adjacent step-wise enlargement or the outlet.
In one specific embodiment, the intermediate throat portion has a diameter of about 4 mm, the axial cylindrical surface of a first step-wise enlargements has a diameter of about 5 mm, and the axial cylindrical surface of second and third step-wise enlargements have diameters of about 6 mm and 7 mm respectively. The restriction zone preferably converges from a diameter of about 10 mm to the 4 mm diameter of the throat portion over an axial distance of about 5 mm. Further, the throat portion preferably extends about 13 mm, the cylindrical surfaces of first and second step-wise enlargements extend about 3 mm in the axial direction, and the cylindrical surface of a third step-wise enlargement extends about 4 mm in the axial direction.
The number of nozzle stages separated by inspiration zones can be varied as desired.
In use with embodiments in accord with the disclosure in U.S. Pat. No. 5,735,468 I have found that in the environment of internal combustion engines a minimum quantity of pressurised air is required to atomize a liquid fuel to a desired particle size. In one prototype this has been established at less than 1% stoichiometric air at 100 psi. That pressurised air is forced through an injector to shear droplets from the conical sheet of fuel with the resultant fuel/air mixture exiting via a delivery nozzle in accord with an embodiment of the present invention.
The addition of premix air which is a minimum quantity of air necessary (when combined with primary air which effects a shearing action of the fuel within the injector body) that facilitates a preparation of a high quality premix for good combustion. The quantity of premix air including atomizing air is normally approximately 5% of the total required for a stoichiometric mixture.
With the further addition of vaporization air (tertiary air) it is possible to vaporize the fuel and give further premix to enhance combustion. Vaporization air is understood to mean the minimum quantity of air necessary (when combined with primary and secondary air) to vaporize the fuel and give further premix to enhance combustion. Such tertiary air can be inspirated into the fuel/air mixture via the inspiration zone or via radially disposed air inlets on a shroud extending past the outlet of the nozzle assemblies. Of course, as stated above, the number of nozzle assemblies can be varied as desired.
I have found that a multiple nozzle arrangement in accord with the present invention not only ameliorates fuel film adherence but also creates good mixing and reduces the velocity of and broadens the fuel air mixture allowing entry of further air into the mixture.
A secondary air nozzle can be attached to an inlet manifold of internal combustion engine or used to entrain other fuels or both fuel and air.
When used in the environment of a pressurized injector of the form disclosed in U.S. Pat. No. 5,735,468 the efficiency of a nozzle of the present invention is not dependent on a negative pressure generated by an engine which can be the case for, say, air-assisted injectors.